Modeling the selective catalytic reduction of NO x by ammonia over a Vanadia-based catalyst from heavy duty diesel exhaust gases Byoung Kyu Yun, Man Young Kim * Department of Aerospace Engineering, Chonbuk National University, 664-14 Duckjin-Dong, Duckjin-Gu, Jeonju, Chonbuk 561-756, South Korea highlights < To find the reaction parameters for LH mechanism over a commercial V2O5 catalyst. < To investigate the effects of various parameters on the SCR NO X conversion. < To present benchmark solutions on SCR behavior with diesel exhaust environments. article info Article history: Received 30 July 2011 Accepted 30 May 2012 Available online 15 June 2012 Keywords: NO x Selective catalytic reduction (SCR) DeNOx Ammonia Diesel exhaust gas abstract A numerical simulation for prediction of NO X conversion over a commercial V 2 O 5 catalyst with NH 3 as a reductant was performed for a heavy duty diesel engine applications. The chemical behaviors of the SCR reactor are described by using the global NO X kinetics including standard, fast, and NH 3 oxidation reactions with the LangmuireHinshelwood (LH) mechanism incorporated into the commercial Boost code. After introducing mathematical models for the SCR reaction with specific reaction parameters, the effects of various parameters such as space velocities, the O 2 ,H 2 O, NO 2 , and NH 3 concentrations on the NOx conversion are thoroughly studied and validated by comparing with the experimental data available in the literature. It is found that NO X conversion increases with decreasing space velocity, H 2 O concentration, and NH 3 /NO X ratio, and increasing O 2 concentration and NO 2 /NO X ratio. The study shows that not only is the present approach adopted is flexible in treating performance of the commercial V 2 O 5 based SCR catalyst, it is also accurate and efficient for the prediction of NO X conversion in diesel exhaust environments. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Due to growing concerns about protecting the environment and human health, the NO x emission standards from heavy duty diesel engines have been continuously tightened over the years throughout the world [1]. Stringent NO x emission standards for heavy duty diesel engines necessitate clean diesel technology and the application of highly efficient exhaust gas aftertreatment systems [2]. Several approaches seem to be technically feasible, such as cooled EGR, common rail fuel injection, LNT, LNC, and SCR DeNOx systems. Among others, the SCR system with urea or NH 3 as a reductant is seen as one of the most promising technologies for adhering to the Euro V and VI NO x emission standards for heavy duty diesel engines [3e9]. At low temperature (<250  C), the SCR reaction, such as stan- dard, fast and slow SCR reaction, dominate over Pt SCR, SCR DeNOx performance increases with increasing exhaust gas temperature. At about 225e250  C, the oxidation of NH 3 to NO x and H 2 O becomes dominant. To utilize the Pt SCR catalyst, one must control the process gas temperature to be above approximately 200  C to avoid NH 4 NO 3 formation, but not to exceed about 225  C, where the catalyst loses its selectivity toward the NO x reduction reaction. Consequently, the use of Pt SCR technology has been rather limited [10]. In addition, Fe zeolite SCR catalysts which are commercially available for stationary applications is known to be operated at temperatures up to 600  C. When NO x is present, this catalyst does not oxidize NH 3 to NO x . Fe zeolite SCR may be prone to stability problems when exposed to high temperatures in the presence of H 2 O. At exposure temperatures above 600  C, in a high H 2 O concentration process stream, zeolites SCR tend to deactivate by de-alumination whereby the Al þ3 ion in the SiO 2 eAl 2 O 3 framework migrates out of the structure. This leads to permanent deactivation and, in extreme cases, collapse of the crystalline structure. A different type of a low temperature zeolite SCR has been developed for mobile diesel engine applications. When used as an SCR * Corresponding author. Tel.: þ82 63 270 2473; fax: þ82 63 270 2472. E-mail address: manykim@jbnu.ac.kr (M.Y. Kim). Contents lists available at SciVerse ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng 1359-4311/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.applthermaleng.2012.05.039 Applied Thermal Engineering 50 (2013) 152e158